A forthcoming paper in Climate of the Past finds the annual sea ice duration around the west Antarctic Peninsula has markedly increased over the past 7,000 years. The authors attribute the changes to "decreasing mean annual and spring [solar] insolation despite an increasing summer insolation" and to ENSO variability changes. In addition, the authors find the temperature of the Antarctic Peninsula has dropped ~2C over the past 9000 years.

Second graph from top shows decrease in temperature over past 9000 years. Third graph from top shows the proxy for sea-ice and shows a marked increase over the past 7000 years.

J. Etourneau1,*, L. G. Collins1, V. Willmott2, J. H. Kim2, L. Barbara3, A. Leventer4, S. Schouten2, J. S. Sinninghe Damsté2, A. Bianchini4, V. Klein1, X. Crosta3, and G. Massé11Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, UMR7159, CNRS/UPMC/IRD/MNHN, 4 Place Jussieu, 75252 Paris, France2Royal Netherlands Institute for Sea Research, Department of marine Biogeochemistry and toxicology, 1790 Den Burg, Texel, The Netherlands3EPOC, UMR5805, CNRS, Université Bordeaux 1, Avenue des Facultés, 33405 Talence, France4Colgate University, Department of Geology, 13 Oak Drive, 13346 Hamilton, USA*current address: Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061, JapanAbstract. The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0–200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep basin. Employing a multi-proxy approach, we derived new Holocene records of sea ice conditions and upper water column temperatures, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEXL86for temperature) and micropaleontological data (diatom assemblages). The early Holocene (9000–7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~ 7000–3000 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~ 3000 yr) was characterized by more variable temperatures and increased sea ice presence, accompanied by reduced local primary productivity likely in response to a shorter growing season compared to the early or mid-Holocene. The stepwise increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation despite an increasing summer insolation. We postulate that in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of El Niño-Southern Oscillation (ENSO). However, between 4000 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time.

A paper published today in Climate of the Past finds Antarctic sea ice extent was much less than the present during the last interglacial period ~120,000 years ago. According to the authors, "During the last interglacial, the [sea ice proxy at 2 sites in Antarctica] are only half of the Holocene levels, in line withhigher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean."

Top graph shows temperature proxy from 2 drilling sites. Horizontal axis is thousands of years before the present. Temperatures were higher than the present during the interglacial ~120,000 years ago. Bottom 2 graphs show a proxy for Antarctic sea ice was only about half of Holocene levels.

S. Schüpbach1,2,3, U. Federer1,2, P. R. Kaufmann1,2, S. Albani4, C. Barbante3,5, T. F. Stocker1,2, and H. Fischer1,21Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland2Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland3Environmental Sciences, Informatics and Statistics Department, University of Venice, Venice, Italy4Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA5Institute for the Dynamics of Environmental Processes – National Research Council, Venice, ItalyAbstract. In this study we report on new non-sea salt calcium (nssCa2+, mineral dust proxy) and sea salt sodium (ssNa+, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa2+ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa2+ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data.

The availability of multiple East Antarctic nssCa2+ records also allows for a revision of a former estimate on the atmospheric CO2sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO2 increase during T1. During the last interglacial, ssNa+ [sea ice proxy] levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean. In contrast, Holocene ssNa+ flux in Talos Dome is about the same as during the last interglacial, indicating that there was similar ice cover present in the Ross Sea area during MIS 5.5 as during the Holocene.